Memoir: How to account for the continued fascination that Graham Greene, the man as well as the writer, holds for the reading public? A clutch of biographies, some of them venomous, have appeared since his death, while the delayed third volume of Norman Sherry's elephantine official Life is expected later this year.
Charge and counter-charge have been made as to the exact shade of Greene's politics, while efforts continue to ascertain what exactly he was up to on those famous travels of his, whether in West Africa during the war or to the Soviet Union in the last years of his life; was he a champion of the Left, or a secret Cold Warrior for the West?
Then there is the matter of his religious beliefs. Having converted to Catholicism at the age of 22, he spent the rest of his life grappling with that great conundrum that faces all believers: if there is a God and he is good, how can it be that the world is so bad? Although Greene resented being dubbed a Catholic novelist - he was, he insisted, a novelist who happened to be a Catholic - the big books he wrote in the 1940s and 1950s were God-tormented affairs. Indeed, so important was the religious theme for Greene's fiction that his friend and fellow-convert Evelyn Waugh teased him by remarking that Greene without God would be like Laurel without Hardy. It is to Greene's credit that it was he who recounted Waugh's witticism, in a memorial tribute to his friend.
How deep did Greene's religion go? Certainly, anyone brought up an Irish Catholic would regard his brand of Catholicism as a very rum thing. He was, for a start, a multiple adulterer. His long, tormented affair with the American Catherine Walston - whose favours he is reputed to have shared briefly with Fr Donal O'Sullivan SJ, a Greene-ish whiskey priest and sometime director of the Irish Arts Council - led him far indeed from the path of righteousness. His biographer, Michael Shelden, admittedly a hostile witness, says that Greene used to boast that he had fornicated behind every high altar in Europe. Other, less bilious commentators suggest that Catholicism was for Greene no more than a pinch of spice in a life of jaded sinning.
Whatever the truth or otherwise of such charges, Greene certainly was a dark and complex personality, haunted from earliest childhood by demons that drove him, on one famous occasion, to dice with his life by playing Russian roulette with a revolver, and which in his middle years sent him wandering through some of the world's most perilous places. He had a taste for danger, both physical and spiritual, and seems to have been fascinated by violence - Michael Shelden goes so far as to insinuate that Greene was the perpetrator of a famous, unsolved murder in Brighton in the 1930s. This is far-fetched, to say the least, but there is no denying the sinister glow that surrounds the image of this secretive, cruelly playful, and sometimes plain cruel, enigmatic figure.
He was genuinely subversive, and although he never ceased to be a middle-class English gentleman, he loved to stick pins in the Establishment bubble: in his acceptance speech for the Shakespeare Prize in Hamburg in 1969 he criticised the Bard for being "the Queen's man" and unwilling to "speak up for the victims". He had a lifelong fondness too for pranks and practical jokes, always a sign of a troubled spirit. Yet he was, in many of his aspects, a good man. His compassion for those whom Frantz Fanon called the wretched of the earth was heartfelt, and throughout his life he used all the influence at his command to help the weak and the downtrodden. However, his urge to promote what he saw as the underdog against the rich and powerful was mixed inextricably with his taste for mischief. For instance, if a large corporation were to ask him to be the final arbiter of a literary prize that it was sponsoring, he would have been perfectly capable of accepting the invitation apparently in good faith, while secretly plotting from the start to overturn the judging process and impose his own choice of winner. In doing so he would, apparently, have seen no hint of dishonourable behaviour.
Yvonne Cloetta, who was Greene's lover and companion for the last three decades of his life, had no doubts that Greene was honourable, as well as kindly, funny and loving. Her question-and-answer portrait of him, "as told to" Marie-Françoise Allain, the daughter of one of Greene's French friends, is artless and wholly charming. Cloetta, a Breton and a Catholic, met Greene in 1959 in Cameroon, where she was living with her husband, an engineer. Although she knew Greene was a world-famous novelist, he was "at that time nothing more to me than the author of a few books I had read and admired". He was on his way back from a six-week stay in a leper colony in the Belgian Congo, where he had been researching what was to become the novel A Burnt-Out Case. Greene himself was going through a period of depression verging on despair, and seems to have seen immediately in this woman the possibility of love and even of spiritual redemption. After the Cameroon encounter he set himself to wooing her, and eventually succeeded in prising her out of her not-very-happy marriage and setting her firmly at the centre of his life, where she remained until his death in 1991.
Cloetta, who died in 2001, was a remarkable woman. She was not an intellectual - but then, neither was Greene - yet she had an instinctive sympathy with the work, and for the man. Being the life partner of an artist is not an easy role, and behind Cloetta's decent reticence can be glimpsed the loneliness of the one who must ever wait outside the locked door, hoping fervently that behind it the words are coming, so that when it opens at the end of the working day the creature that emerges will be at least halfway human and not in search of someone to kill. She loved Greene with simplicity and devotion, and in return he cherished her and depended on her to an almost childlike degree.
"He gave me," she declares, "a soul." What better tribute could one human being pay to another?
Perhaps the most fascinating section of the book is the one entitled 'The Baffling Edge of Espionage'. Greene was, Cloetta says, a man with "different compartments in his head", who could be genuinely devout yet still frequent brothels - she recounts a grisly episode in Paris when he took her and another woman friend to a whorehouse, apparently with the intention of setting up a private orgy - and who kept his links with the British Secret Service even as he was championing such figures as Fidel Castro.
"Graham's secret," Cloetta shrewdly observes, "was his passion for secrecy." He stayed in contact with his friend Kim Philby right up to the time of Philby's death, and may have been a conduit between Philby and British intelligence, if Philby was a double, or triple, agent, as some suspect he was.
Greene had worked for MI6 during the war, and there are those who insist that he, too, remained a spy all his life. Was he spying for the British on those trips to Cuba and to Moscow during the Cold War? He would have enjoyed the joke: the international promoter of left-wing causes returning to some anonymous room in St James's to report on what he had found out about the doings of Castro or Brezhnev. Having hedged her way past her interlocutor's more probing questions on the issue, Cloetta ends with a startlingly frank assertion: "Graham has left us, taking his secrets with him. But what I can tell you is that, to the very end, he worked with the British Services."
There is also a tantalising reference to an occasion "when he went off on some sort of mission to Northern Ireland", about which he was "quite worried",apparently fearing for his own safety. The minds of Irish readers will go back to the curious and shady figure of Sir Maurice Oldfield, spymaster and reputed model for John Le Carré's George Smiley, whom Margaret Thatcher sent to Northern Ireland as head of British army intelligence. Was there a connection?
Probably Greene's novels are not as widely read now as they once were. Their blend of existential bleakness and queasy religiosity appealed directly to middlebrow tastes in a time of postwar guilt and nuclear terror, but may seem outdated in our more ambiguously troubled age. It was Le Carré who remarked that Greene was essentially a "Thirties writer" - a charge that troubled Greene deeply - but it would surely be more accurate to say that he was a writer of the 1940s and 1950s.
Marie-Françoise Allain remarks on Greene's "nondescript" prose style, "so hard to define or classify", which yet - or therefore - could speak directly to millions of readers. Although he took a certain pride in his achievement, Greene had no grand pretensions. "I am not a genius," he says in Cloetta's Carnet rouge, the notebook in which she recorded many of his obiter dicta. "I am a craftsman who writes books at the cost of long and painful labour."
It is a modest claim, and a true one.
• John Banville's most recent book is Prague Pictures: Portraits of a City, published by Bloomsbury